The assembly of the windshield, rear window and other glass elements of a vehicle to their associated body flanges is an important operation in the manufacture of vehicles, particularly from a safety standpoint. The federal government requires vehicles to pass a windshield retention test, and the materials which are used to assemble the windshield to the body flanges of the vehicle must be properly applied to pass the test and avoid expensive recalls.
The preparation of the windshield and associated body flange of a vehicle for assembly involves a number of operations. With respect to the windshield, glass manufacturers supply automotive windshields with a "blackened area", i.e., an area of predetermined width along the marginal edge of the windshield which is covered with a black, ceramic frit having a roughened surface. It is the responsibility of the automotive manufacturer to prepare this blackened area for assembly to the body flange of the vehicle. First, a clear glass primer material is applied to the blackened area, usually with a wet brush manipulated by a robot or other automated brush mover. Preferably, a felt wick is dragged by the robot immediately behind the wet brush to wipe dry the clear glass primer, and to force the clear glass primer into the roughened surface of the blackened area. The clear glass primer prepares the blackened area for receipt of a coat of black glass primer material as described below.
One problem which has been experienced with the application of clear glass primer onto the blackened area of the windshield is that the primer is not readily visible, and it is difficult to determine how much clear glass primer has been applied and whether the desired amount of the surface area of the ceramic frit has been covered. An inadequate amount or film build of clear glass primer, and/or an incomplete covering of the surface area having the ceramic frit, can result in a failure of the windshield retention test after the windshield is installed.
The next step in the preparation of the windshield for assembly to the vehicle body flange involves the application of a black glass primer over the area which had been previously coated with the clear glass primer. One method of applying the black glass primer to the windshield involves a manual operation using a flow brush or the like. This method is labor-intensive, and human applicators are prone to dripping some of the black glass primer from the brush onto areas outside of the blackened, ceramic frit. Such drips onto the clear portion of the glass are unacceptable and may require rejection of the windshield for use.
Another means of applying the black glass primer onto the marginal edge of the windshield is disclosed, for example, in U.S. Pat. No. 4,857,367 to Thorn et al. This patent discloses an apparatus which comprises a liquid spray nozzle, an air nozzle and a vacuum device which are movable as a unit upon a robot arm relative to the marginal edge of a windshield. The liquid nozzle sprays atomized black glass primer material in a triangular pattern onto the edge of the windshield. In order to prevent oversprayed, atomized black glass primer from being deposited onto the clear portion of the windshield, the air nozzle directs a stream of air from the interior of the windshield outwardly so as to force any oversprayed primer particles away from the interior or clear portion of the windshield. The vacuum device is located beneath and alongside the peripheral edge of the windshield to draw a vacuum thereat and collect the oversprayed primer particles which do not adhere to the glass.
While systems of the type disclosed in U.S. Pat. No. 4,857,367 are intended to avoid the drip-page problem obtained with manual application of the black primer, it has been found that the application of at least some black glass primer onto the clear portion of the windshield can still occur. The vacuum device is not completely effective in collecting the oversprayed, atomized black glass primer discharged from the liquid nozzle, and some of this oversprayed black glass primer can fall onto the clear portion of the windshield.
Another aspect of the windshield assembly operation is the preparation of the body flange of the vehicle which mounts the windshield. A black metal primer is applied to this body flange, typically using a flow brush and/or an atomized spray type of coating dispenser such as a spray gun, both of which are manipulated manually by an operator. The application of the black metal primer must be performed with great care because the exterior surfaces of the vehicle have received a finish coat of paint before the windshield is installed. Drippage or running of the black primer from the flow brush onto the "Class A" or painted surface of the vehicle presents a major quality control problem. In addition to the drippage problem, manual application of the black metal primer with a brush can also result in too much material being applied to the body flange, the formation of streaks thereon and/or a film build-up along one or more areas of the flange. While dispensers such as spray guns which produce an atomized spray of the black metal primer can be utilized along some areas of the body flange of the vehicle, the problem of oversprayed primer from such guns prohibits their use anywhere near the finished, painted surface of the vehicle.